Also known as: NAC

What does it do? N-acetyl cysteine (NAC) is an altered form of the amino acid cysteine, which is commonly found in food and synthesized by the body. NAC helps break down mucus. Double blind research has found that NAC supplements improved symptoms in individuals with bronchitis.^{1 2}

NAC helps the body synthesize glutathione—an important antioxidant. In animals, the antioxidant activity of NAC protects the liver from exposure to several toxic chemicals. NAC also protects the body from acetaminophen toxicity and is used at very high levels in hospitals for that purpose.

Where is it found? Cysteine, the amino acid from which NAC is derived, is found in most high-protein foods. NAC is not found in the diet.

N-acetyl cysteine has been used in connection with the following conditions (refer to the individual health concern for complete information):

Who is likely to be deficient? Deficiencies of NAC have not been defined and may not exist. Deficiencies of the related amino acid cysteine have been reported in HIV-infected patients.³

How much is usually taken? Healthy people do not need to supplement NAC. Optimal levels of supplementation remain unknown, though much of the research uses 250–1,500 mg per day.

Are there any side effects or interactions? When NAC is taken by mouth, one trial reported nausea, vomiting, headache, dry mouth, dizziness, or abdominal pain, in 19% of people in the study.⁴ These symptoms have not been consistently reported by other researchers, however.

One small study found that daily amounts of 1.2 grams or more could lead to oxidative damage.⁵ Extremely large amounts of cysteine, the amino acid from which NAC is derived, may be toxic to nerve cells in rats.

NAC may increase urinary zinc excretion.⁶ Therefore, supplemental zinc and copper should be added when supplementing with NAC for extended periods. A good multi vitamin would contain these nutrients.

Within Healthnotes Online, information about the effects of a particular supplement or herb on a particular condition has been qualified in terms of the methodology or source of supporting data (for example: clinical, double blind, meta-analysis, or traditional use). For the convenience of the reader, the information in the table listing the supplements for particular conditions is also categorized. The criteria for the categorizations are: “Primary” indicates there are reliable and relatively consistent scientific data showing a health benefit. “Secondary” indicates there are conflicting, insufficient, or only preliminary studies suggesting a health benefit or that the health benefit is minimal. “Other” indicates that an herb is primarily supported by traditional use or that the herb or supplement has little scientific support and/or minimal proven health benefit.

References:

1. Boman G, Bäcker U, Larsson S, et al. Oral acetylcysteine reduces exacerbation rate in chronic bronchitis: a report of a trial organized by the Swedish Society for Pulmonary Diseases. Eur J Respir Dis 1983;64:405–15.
2. Multicenter Study Group. Long-term oral acetylcysteine in chronic bronchitis. A double-blind controlled study. Eur J Respir Dis 1980;61:111:93–108.
3. de Quay B, Malinverni R, Lauterburg BH. Glutathione depletion in HIV-infected patients: role of cysteine deficiency and effect of oral N-acetylcysteine. AIDS 1992;6:815–19.
4. Tattersall AB, Bridgman KM, Huitson A. Acetylcysteine (Fabrol) in chronic bronchitis—a study in general practice. J Int Med Res 1983;11:279–84.
5. Kleinveld HA, Demacker PNM Stalenhoef AFH. Failure of N-acetylcysteine to reduce low-density lipoprotein oxidizability in healthy subjects. Eur J Clin Pharmacol 1992;43:639–42.
6. Brumas V, Hacht B, Filella M, Berthon G. Can N-acetyl-L-cysteine affect zinc metabolism when used as a paracetamol antidote? Agents Actions 1992;36:278–88.